Hello,
I understood the problem that I encountered:
I burned the knoppix.iso that I have remastered on a RW-CD, and after a while, I suspected that there was a problem
with the RW-CD and knoppix.
To check out that I thought I copied my original R-CD knoppix(xhich works fine) on the RW-CD and when I booted on the RW-CD
I obtained the same problem: "can't find knoppix filesystem ...".
Finally I put my knoppix.iso (remastered) on a pendrive and knoppix booted like charm.
(But not all pendrives are able to boot ....)

hth